24 Sectors DTC Control with Fuzzy Hysteresis Comparators for DFIM Fed by the Three-level NPC Inverter

This article presents 24 sectors direct torque control (DTC) with fuzzy hysteresis comparators for the doubly-fed induction motor (DFIM) using a three-level neutral point clamped (NPC) inverter. The designed DTC technique of the DFIM combines the advantages of the DTC strategy and fuzzy logic controller. The reaching conditions, stability, and robustness of the DFIM with the designed DTC technique are guaranteed. The designed DTC technique is insensitive to uncertainties, including parameter variations and external disturbances in the whole control process. Finally, the designed DTC technique with fuzzy hysteresis comparators is used to regulate the electromagnetic torque and the flux of the DFIM fed by the three-level NPC inverter and confirms the validity of the designed DTC technique. Results of simulations containing tests of robustness and tracking tests are presented.

Analysis and Simulation of Current-source Flyback Inverter with Efficient BCM Control Strategy

The Flyback inverter is a single-stage power inverter which represent an attractive solution for photovoltaic (PV) grid-tied inverter application. The main advantages of a current-source flyback inverter are high power density and high efficiency due to its small, as well as low total harmonic distortion (THD) operation. However, a flyback topology works with Discontinuous Conduction Mode (DCM) control strategy has lower efficiency and poor THD values. In this paper, an efficient current-source flyback inverter topology works with Boundary Conduction Mode (BCM) control strategy is presented. Besides, an efficient incremental conductance (IC) maximum power point tracking (MPPT) is used to extract the maximum power from the PV module. To verify the proposed control a power simulator (PSIM) software is used. As a result, the simulation results indicates that the BCM control is more efficient than the DCM method for various weather conditions. Finally, the proposed BCM strategy is compared with DCM control in terms of THD and thus it is achieved lower THD contain in the injection current of grid.

Phase Noise Reduction Technique for ISM Band LC Oscillator Using Tail Current

This paper presents low phase noise, precise frequency tuning range LC Voltage controlled Oscillator (VCO) circuit of Phase lock loop, to support - IEEE 802.11a/b/g, Bluetooth, Zigbee and IEEE 802.15.4., operating on 2.4GHz ISM band (Industrial, Scientific, Medical). The presented circuit is implemented in Cadence virtuoso environment and using GPDK090 Library of 90nm CMOS Technology. The presented VCO is tuned at 2.4GHz frequency with tuning range of 80MHz. The measured Phase noise is -126.3dBc/Hz at 1MHz offset frequency. The total power consumption of the presented VCO is 4.7mw at 1V power supply.

Systematic Structural and Optical Characterization of TiO2 Nanofibres Synthesised by Electrospinning

TiO2 nanofibres were synthesised by means of the electrospinning technique, which were annealed at high temperatures to achieve the crystalline phase transformation. The chemical stoichiometry of electrospun TiO2 nanofibres was estimated by EDS, finding that at low annealing temperatures excess of oxygen was detected and at high temperatures excess of titanium that originates oxygen vacancies. TEM images show clearly the formation of TiO2 nanofibres that exhibit a homogeneous and continuous aspect without the presence of crystalline defects, whose surface morphology depends strongly on the annealing temperature. The crystalline phase transformation was studied by Raman spectroscopy, which revealed that annealed TiO2 nanofibres showed a crystalline phase transformation from pure anatase to, first a mix of anatase-rutile, then pure rutile as the annealing temperature increased, which was corroborated by X-ray diffraction and high-resolution TEM microscopy. The average grain size, inside the nanofibres, increased with the crystalline phase transformation from 10 to 24 nm for anatase-TiO2 and from 30 to 47 nm for rutile-TiO2, estimated by using the Scherrer-Debye equation. The band gap energy (Eg), obtained from optical absorption spectra, decreases monotonically, where a local minimum is observed at 700 °C, which is ranged in 3.75  Eg  2.42 eV, caused by the anatase → rutile crystalline phase transformation. The photoluminescence shows that radiative bands present a gradual red-shift as the annealing temperature increases due to the continuous change of Eg.

Microcontroller Based High Voltage, High Speed Trigger Control Circuit for SMARTEX-C

Microcontroller based trigger control circuit for fast pulsing of electrode potentials on wide range of time scales has been designed, installed, and tested for electron plasma experiments which are carried out in partial toroidal trap SMall Aspect Ratio Toroidal Electron plasma EXperiment in C – shaped geometry (SMARTEX – C), a device to create and confine non-neutral plasma (electron plasma). The sequence of trap operation is inject-hold-dump for which electrodes need to be pulsed with applied voltages at a high switching speed of few nanoseconds. Also this sequence of operation needs to be controlled over a very wide range of time scales from few microseconds to few seconds. As the available COTS (Commercial-Off-The-Shelf) high voltage DC power supplies generally do not provide this feature of fast switching at nanosecond time scale, MOSFET based circuit is developed which provides fast switching in the range of 20 – 100 nanoseconds of high voltages (200Vdc - 500Vdc) of multiple electrodes. The timing pulse widths of these trigger pulses are controlled using a microcontroller-based circuit. This experimental set-up also requires the triggering of a high current dc power supply used for an Electro-magnet (Toroidal Field Coil) to generate a toroidal magnetic field, at the start of this experiment. For this purpose, a Silicon Controlled Rectifier (SCR) based circuit is used. The gate pulse to trigger the SCR circuit is also generated from this microcontroller-based circuit. National Instrument’s LabVIEW software based Graphical User Interface (GUI) is developed for triggering the SCR and electrodes with a programmable time period through the serial link.

A Compact Fractal-Shaped O-Ring Monopole Antenna for Modern Broadband Wireless Applications

In this letter, the design of a compact planar Fractal-shaped O-ring monopole antenna based on the Sierpinski carpet concept is studied and proposed for modern broadband wireless applications. The planar fractal-shaped O-ring monopole antenna is on the basis of Sierpinski category construction and then modifies the state of the plane inward with a radius of 27mm over the two iterations. The antenna structure is low profile and easy to be fabricated, and it has performed the simulation and measurement with the result VSWR ≤ 2 that can achieve a wide impedance bandwidth 636% from the frequency band 1.57GHz ~ 10GHz. The geometric scale factor of the Sierpinski fractal is according to the same scale element that defines the geometrical self-similarity. In our experiments, the results show that use of fractal-shaped O-ring into monopole antenna structure can effectively improve input impedance matching, and obtain a larger bandwidth and better radiation pattern, while also having predictable multi-band characteristics.

A High Gain, High BW OP AMP with Frequency Compensation Techniques at 65 nm Technology

OP-AMPs finds applications in different domains of electronics engineering including communications. There has been several OP-AMP configurations realized in the last decades for different target applications. But with the evolution of communication standards, to meet the demand for high data rate over the years, requirement for a high frequency and high BW OP-AMP is gaining attention. This makes the design challenge much higher. This paper presents a two-stage CMOS amplifier which uses frequency compensation method to facilitate higher BW. Different parameters like Gain, Gain band width product (GBWP), Phase Margin and Total Power dissipation are considered in this design. A step-by-step procedure for an efficient amplifier design is followed using frequency compensation. We have achieved a gain-bandwidth product (GBWP) of 110 MHz that is capable of driving large capacitive loads. It also achieves 77.7 dB gain with a phase margin of 60o.

Application of Statecharts in Buck-Boost DC-DC Converter Simulation

A very attractive and relatively simple option to simulate a DC-DC converter is to use a hybrid model. In this case, the need to use very small simulation steps (as those necessary to simulate models carried out at the physical level) is avoided. Furthermore, unlike the averaged state-space models, it has the advantage that the model is valid throughout the entire working range of the converter and for both conduction modes (continuous and discontinuous). By simulating several renewable energy conversion systems incorporating DC-DC converters, the authors have discovered the true potential of this modeling method. Despite its inherent advantages, this approach to DC-DC converters simulation is not as widely adopted as it should be. This work tries to encourage the reader of its use in certain typical situations. In this article the implementation of the hybrid model of the DC-DC Buck-Boost converter, using Statechart techniques, is performed. This model was written in the Stateflow language, a tool from the MATLAB®/Simulink environment, and allowed the creation of a building block formed by the described converter model with adequate interfaces to the SimPowerSystem and Simulink environments. The block is validated by comparing simulation results, realized under different operating conditions, with calculations done employing well-known and proven formulas. As an example of the use of the presented block, a buck-boost DC-DC converter with voltage and current control loops is simulated, corroborating its correct performance

On a Quasi Optimal Algorithm for Analog Circuits Optimization

An analog circuit design methodology based on applications of control theory is the basis for constructing an optimal or quasi-optimal design algorithm. The main criterion for identifying the required structure of the algorithm is the behavior of the Lyapunov function, which was decisive for the circuit optimization process. The characteristics of the Lyapunov function and its derivative are the basis for finding the optimal structure of the control vector that determines the structure of the algorithm. A block diagram of a quasi-optimal algorithm that implements the main ideas of the methodology is constructed, and the main characteristics of this algorithm are presented in comparison with the traditional approach

Ferromagnetic Schottky Contact for GaN Based Spin Devices

In this paper, ferromagnetic Schottky contacts for GaN based spin injection are being studied. The electrical characterization of this Co/n-GaN and Fe/n-GaN Schottky contacts showing the zero-bias barrier height comes closer to unity as the temperature is increased. Also, the Richardson constant is extracted for this Schottky contact. Both the zero-bias barrier height and the Richardson constant are verified both experimentally as well as theoretically. Thus, this Schottky contacts will serve as spin injector for GaN based spin devices specifically for GaCrN based devices